This invention relates generally to machine tool spindles having a drawbar disposed therein for threaded engagement onto or off of a toolholder inserted in the spindle bore and, more specifically, to a machine tool spindle having a drawbar therein which is rotatably driven by the spindle drive motor.
Present day numerically controlled milling machines, such, as the Kearney & Trecker Model Data Mill 700 milling machine, for example, having a cutting tool-holding spindle therein which is driven by a spindle drive motor through a suitable gearing arrangement. Extending coaxially into the bore of the spindle is a drawbar which is rotatably driven for threaded engagement into or out of the shank of a toolholder disposed in the bore of the spindle to engage and to disengage, respectively, the toolholder in the spindle. Heretofore, separate motor drive systems have been employed within the machine for rotatably driving the drawbar within the spindle and for rotatably driving the spindle itself. A motor drive system well suited for rotatably driving the drawbar to thread it into or out of the toolholder shank is described and claimed in U.S. Pat. No. 4,199,286 issued to Edward E. Kirkham and assigned to the assignee of the present invention.
Employing separate drive systems for rotatably driving the drawbar within the spindle and for rotatably driving the spindle itself necessitates separate motors which not only increases machine tool cost, but also increases machine tool complexity since separate controls for each motor are required. Such increased machine tool complexity invariably leads to greater repair expenses should service ever become necessary.
It is thus an object of the present invention to provide a machine tool spindle in which the drawbar and spindle are rotatably driven from a single source of rotational energy.
It is another object of the present invention to provide a machine tool spindle having a drawbar therein rotatably driven by the machine tool spindle drive motor.